The invention relates to a method for assessing the range of a run-flat system; here, a run-flat system designates a unit comprising, at least for each wheel, a tire, a deflation alarm, and means for supporting the tread of the tire in the event that the tire is deflated.
The method according to the invention also allows the conditions for re-using the run-flat system to be evaluated; these conditionsxe2x80x94after travelling on a flat tire or on a tire at very low pressurexe2x80x94may be simply the re-use of the system as it is after repairing and reinflating the tire, or changing of the tire, or replacement of the safety bearing, or both.
It is known that the loss of pressure in a tire may be abrupt, for example following a burst, or very slow, for example after a puncture, but in all cases there is a risk of loss of control of steering of the vehicle. Devices for so-called xe2x80x9crun-flatxe2x80x9d operation have thus been proposed, which generally comprise an annular insert bearing mounted inside the tire to limit the deflection of the latter and where appropriate to prevent the phenomenon of bead unseating, that is to say, the displacement of a bead towards the inside of the rim, which causes the tire to be unseated from the rim.
A device of this kind is described, for example, in U.S. Pat Nos. 5,634,993 and 6,092,575 to Drieux et al., and U.S. Pat. No. 5,891,279 to Lacour, which are owned in common with the present application.
There have also been proposed tires whereof the structure, in particular of the sidewalls, is highly reinforced in order to allow them to travel at low pressure or no pressure. One example of tires of this kind, called xe2x80x9cself-supportingxe2x80x9d, is given in U.S. Pat. No. 6,026,878 to Zhang et al.
Paradoxically, these modern devices for run-flat operation are so effective that the driver does not easily realize that the pressure in one of the tires of the vehicle has gone down. These systems must therefore include apparatus for measuring the pressure of the tires, the main function of which is to alert the driver as soon as the pressure in a tire falls below a predetermined threshold.
These run-flat systems, which are based on the use of means for supporting the tread of the tire in the event that the tire deflates arranged within or outside the tire, according to tire manufacturers, currently allow travel under run-flat conditions at limited speed (in the order of 80 km/h at most) and for a distance which is also limited (in the order of 200 km).
In reality, these limit values are determined in very harsh conditions of use for the vehicles and the run-flat systems, and they very often underestimate the potential for use in actual conditions for these systems and the range they can offer to users.
The object of the invention is in particular to continuously indicate to the driver an estimate of the actual range available in a tire after a pronounced loss of pressure, in accordance with the actual conditions of travel.
The present invention therefore enables a continuous indication to the driver of the actual available range; where appropriate, it warns the driver that the tire has gone beyond a maximum distance and that the driver should stop; finally, it specifies the conditions for re-use of the driver""s run-flat system.
To obtain this result, the invention makes use of the processing of data coming from different sensors and representing significant parameters of the relevant run-flat system and the vehicle.
The method according to the invention for assessing the range of a run-flat system which is fitted to a vehicle, the system comprising, at least for each wheel, a tire, a deflation alarm and means for supporting the tread of the tire in the event that the tire is deflated, is characterized in that, from the moment when the deflation alarm has detected a predetermined threshold of deflation:
the distance traveled and a parameter C(t) characteristic of the travel conditions are measured periodically;
as a function of C(t) and the distance traveled over the period xcex94t, a quantity characteristic of a potential elementary damage to the system over the said elapsed period xcex94t is determined;
an estimate of the overall damage is calculated from a combination of the elementary damages calculated since the start of run-flat travelling; and
there is transmitted to the driver of the vehicle a quantity linked to this estimate of overall damage to the run-flat system.